Semiconductor device and method for manufacturing the same

Abstract

To provide a highly reliable semiconductor device by giving stable electrical characteristics to a transistor including an oxide semiconductor film. A gate electrode layer is formed over a substrate, a gate insulating film is formed over the gate electrode layer, an oxide semiconductor film is formed over the gate insulating film, a conductive film is formed over the oxide semiconductor film, so that a region in vicinity of an interface with the oxide semiconductor film in contact with the conductive film is made amorphous, heat treatment is performed, the conductive film is then processed to form a source electrode layer and a drain electrode layer, and a part of the amorphous region in the oxide semiconductor film which is exposed by formation of the source electrode layer and the drain electrode layer is removed.

What is claimed is: 
     
       1. A semiconductor device comprising:
 a gate electrode; 
 a gate insulating film over the gate electrode; 
 an oxide semiconductor film over the gate insulating film, wherein the oxide semiconductor film comprises a first film in contact with the gate insulating film and a second film over the first film; 
 a source electrode and a drain electrode over the second film; and 
 an insulating film over the oxide semiconductor film, the source electrode, and the drain electrode, 
 wherein, in the oxide semiconductor film, a proportion of a crystal part to an amorphous part in a first region in vicinity of an interface with any of the source electrode and the drain electrode is lower than a proportion of a crystal part to an amorphous part in a second region that is a remaining region of the oxide semiconductor film except the first region, 
 wherein, in the oxide semiconductor film, a thickness of a third region overlapping with one of the source electrode and the drain electrode and a thickness of a fourth region overlapping with the other of the source electrode and the drain electrode are larger than a thickness of a fifth region overlapping with neither the source electrode nor the drain electrode, 
 wherein the third region, the fourth region and the fifth region overlap with the gate electrode, 
 wherein the fifth region is positioned between the third region and the fourth region in a channel length direction, 
 wherein each of the third region and the fourth region is positioned between parts of the fifth region in a channel width direction, and 
 wherein the insulating film is in direct contact with a top surface of the first film in the fifth region. 
 
     
     
       2. The semiconductor device according to  claim 1 ,
 wherein hydrogen concentration in the first region is greater than or equal to 5×10 18 /cm 3 . 
 
     
     
       3. The semiconductor device according to  claim 1 ,
 wherein hydrogen concentration in the second region is less than 5×10 18 /cm 3 . 
 
     
     
       4. The semiconductor device according to  claim 1 ,
 wherein the crystal part is a c-axis aligned crystalline oxide semiconductor. 
 
     
     
       5. The semiconductor device according to  claim 1 ,
 wherein the oxide semiconductor film comprises a material selected from indium, gallium, zinc, and a combination thereof. 
 
     
     
       6. The semiconductor device according to  claim 1 , further comprising:
 an oxide insulating film including an oxygen-excess region over the oxide semiconductor film, the source electrode, and the drain electrode; and 
 an aluminum oxide film over the oxide insulating film. 
 
     
     
       7. The semiconductor device according to  claim 1 ,
 wherein an entire portion of the first region is amorphous. 
 
     
     
       8. A semiconductor device comprising:
 a gate electrode; 
 a gate insulating film over the gate electrode; 
 an oxide semiconductor film over the gate insulating film, wherein the oxide semiconductor film comprises a first film in contact with the gate insulating film and a second film over the first film; 
 a source electrode and a drain electrode over the second film; and 
 an insulating film over the oxide semiconductor film, the source electrode, and the drain electrode, 
 wherein, in the oxide semiconductor film, a proportion of a crystal part to an amorphous part in a first region in vicinity of an interface with any of the source electrode and the drain electrode is lower than a proportion of a crystal part to an amorphous part in a second region that is a remaining region of the oxide semiconductor film except the first region, 
 wherein, in the oxide semiconductor film, a thickness of a third region overlapping with one of the source electrode and the drain electrode and a thickness of a fourth region overlapping with the other of the source electrode and the drain electrode are larger than a thickness of a fifth region overlapping with neither the source electrode nor the drain electrode, 
 wherein the third region, the fourth region and the fifth region overlap with the gate electrode, 
 wherein the fifth region is positioned between the third region and the fourth region in a channel length direction, 
 wherein each of the third region and the fourth region is positioned between parts of the fifth region in a channel width direction, 
 wherein the insulating film is in direct contact with a top surface of the first film in the fifth region, 
 wherein the oxide semiconductor film comprises a material selected from indium, gallium, zinc, and a combination thereof, and 
 wherein the second film has an atomic ratio where an atomic percent of gallium is greater than or equal to an atomic percent of indium. 
 
     
     
       9. The semiconductor device according to  claim 8 ,
 wherein the first film has an atomic ratio where an atomic percent of indium is greater than an atomic percent of gallium. 
 
     
     
       10. The semiconductor device according to  claim 8 ,
 wherein hydrogen concentration in the first region is greater than or equal to 5×10 18 /cm 3 . 
 
     
     
       11. The semiconductor device according to  claim 8 ,
 wherein hydrogen concentration in the second region is less than 5×10 18 /cm 3 . 
 
     
     
       12. The semiconductor device according to  claim 8 ,
 wherein the crystal part is a c-axis aligned crystalline oxide semiconductor. 
 
     
     
       13. The semiconductor device according to  claim 8 , further comprising:
 an oxide insulating film including an oxygen-excess region over the oxide semiconductor film, the source electrode, and the drain electrode; and 
 an aluminum oxide film over the oxide insulating film. 
 
     
     
       14. The semiconductor device according to  claim 8 ,
 wherein an entire portion of the first region is amorphous.